JPS5952383B2 - RMS conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an effective conversion circuit that converts an effective value of an analog input quantity of electricity into a digital signal.

It may be necessary to convert the effective value of an analog input electrical quantity into a digital signal.

In this case, in conventional circuits, the input electrical quantity is squared and its average value is taken, the average value, which is an analog signal, is calculated via a square root circuit, and the calculated output is converted from analog to digital. It was However, in such a circuit, since the average value calculation and the square root calculation are performed in an analog circuit, it is difficult to reduce temperature fluctuations and changes over time, and sufficient accuracy cannot be obtained. Another method is to convert the analog signal into a digital signal and then use a digital circuit to perform the specified calculations, but although the accuracy and stability may be good, the circuit size will be large and expensive. There are drawbacks. The present invention solves these drawbacks and realizes an effective value conversion circuit that converts the effective value of an analog input quantity of electricity into a digital signal with a relatively simple configuration.

A detailed explanation will be given below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In Figure 1, 1 is an analog input terminal, 2 is a square circuit,
3 is a pulse time width signal conversion circuit (hereinafter abbreviated as conversion circuit)
, 4 is a timer, 5 is a pulse generation circuit, 6 is an AND gate, 7 is a counter, and 8 is a display. The analog input terminal 1 is coupled to a conversion circuit 3 via a squaring circuit 2, the output of which is coupled to one input of an AND gate 6. The output signal of the timer 4 is coupled to the conversion circuit 3 and the pulse generation circuit 5. The output of the pulse generating circuit 5 is coupled to the other input of the AND gate 6. An analog voltage signal whose effective value is converted into a digital signal is input to the analog input terminal 1.

A squaring circuit 2 squares this analog voltage signal.

For example, a dual slope type circuit is used as the conversion circuit 3, and a pulse duration signal whose length is proportional to the input voltage is obtained at the output. Here, the output signal of the square circuit 2 is averaged. Note that this repetition period Ts is determined by timer 4.
gives. In the pulse generation circuit 5, the frequency is between fo and f.
m pulse signals having a frequency division relationship of o/m are generated. Depending on the time signal sent by the timer 4, this is switched and sent to the output of the pulse generation circuit 5. FIG. 2 shows a time waveform diagram of each part in FIG. B is the output waveform of the conversion circuit 3, and C is the output waveform of the gate circuit 6.
During the first time interval TO after TO has elapsed from the beginning of the sampling period Ts of the conversion circuit 3, the pulse generation circuit 5
Select the signal at frequency FO and send it to the output.

In the second time interval 2t0 following the time interval TO, a signal with a frequency FO/2 is selected and sent to the output. At the next third time interval 3t0, a signal of frequency FO/3 is selected and sent to the output. In this way, control is performed to select a signal with a frequency of FO/m at the m-th time interval MtO. Here, set the time divisions as TO, 2tO, 3tO...
- When changing linearly with MtO, an equal number of pulses will exist in one time segment. This signal is used as the pulse time j width signal (second
When it is applied to the gate circuit 6 along with the signal shown in FIG. 2C, a signal waveform as shown in FIG. 2C is obtained at its output.

The number of pulses shown in C is the pulse time width signal Tx
The number is proportional to the 1/2 power of the length of the high potential duration Tx, that is, the effective value of the analog voltage signal input to the input terminal]. To explain this using a formula, the frequency f changes as FO/2, f0/3...FO/m for each time interval, so if we introduce a parameter p (however, k
1 is a proportional coefficient).

Between parameter p and time t, the length of the time interval is T
Since it changes linearly with O, 2tO, 3tO...MtO, the elapsed time is the accumulation of these (however, K
2 is the proportionality coefficient).

Calculating p from equation (2), we get Substituting this into equation (1), (However, K3 is a proportional coefficient) It can be expressed as

The number of pulses D appearing at the output of this converter is then gated at a frequency which is a function of this time by the high potential duration Tx of the pulse duration signal, so it can be expressed as:
From equation (4), it becomes.

Here, since Tx is proportional to the average value P of the square of the input analog voltage E (K4 is a proportional coefficient), it can be expressed as follows.

That is, it is possible to obtain an effective value conversion circuit in which the number of pulses D obtained at the output is proportional to the square root of the average value of the square of the input analog voltage E, that is, the effective value of the input analog voltage E. The number of pulses D thus obtained is counted by a counter 7 and displayed on a display 8. The input/output relationship of the circuit of the present invention is a broken line approximation of this function, and this situation is shown in FIG.

FIG. 3 shows how the frequency changes with time, with the horizontal axis representing time t and the vertical axis representing the output frequency f of the pulse generating circuit. Each time division TO, 2tO, 3tO・
When the frequency changes stepwise for each time interval, the broken line connecting the midpoints of each time segment becomes the approximate broken line of equation (4). FIG. 4 shows the analog voltage E input to the conversion circuit 3 of the present invention.
''(E''=E2) and the number of pulses D of the output digital signal
The function in equation (6) is a parabola, but it is transformed by a solid line function that is approximated by a broken line.

The finer the time divisions and the higher the pulse frequency, the more the approximation accuracy can be improved.

In this example, in the simplest case, the time division changes as TO, 2tO, 3tO, etc., and the frequency changes as F.
An example was shown in which the values change as O, fO/2, f0/3, etc., but if K and k'' are constants, the length of the time division becomes KtO,
It changes linearly like 2ktO, 3ktO, etc., and the output of the pulse generation circuit changes FO at each time interval accordingly.
/k'', FO/2k'', FO/3k'', etc., the relationships in equations (1) to (6) in the above explanation hold in the same way.

Therefore, even in such a relationship, the present invention can be implemented in the same manner. The configuration of the pulse generation circuit is also not of the switching type as in the above example, but may be of a synthesizer type or any other type.

As described above, according to the present invention, it is possible to realize an effective value conversion circuit that converts the effective value of an analog input quantity of electricity into a digital signal with a high enough precision for practical use with a relatively simple configuration.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a configuration explanatory diagram showing one embodiment of the present invention, Fig. 2 is a waveform diagram of each part in Fig. 1, Fig. 3 is an explanatory diagram of the operation of the pulse generation circuit, and Fig. 4 The figure shows the relationship between analog input signals and digital output signals. 1... Analog input terminal, 2... Square circuit, 3...
・Pulse time width signal conversion circuit, 4... timer, 5...
- Pulse generation circuit, 6... gate circuit, 7... counter, . 8...Display device.

Claims (1)

[Claims] 1. A squaring circuit that squares an analog input signal, a pulse time width conversion circuit that converts the output signal of this squaring circuit into a pulse time width signal, and a pulse time width conversion circuit that converts the output signal of this pulse time width conversion circuit into a pulse time width signal. a pulse generation circuit that generates an equal number of pulse signals for each successive time interval whose time width changes linearly; an output signal of this pulse generation circuit and an output signal of the pulse time width conversion circuit; An effective conversion circuit comprising a gate circuit.